This invention relates to execution of operations from a keyboard. More particularly, this invention relates to method and apparatus for determining which of a number of operations, functions, or other actions associated with a key is to be executed upon pressing of the key.
Electronic keyboards have traditionally assigned one symbol such as a letter mathematical function, numeral, or operator (+,-, etc.) to each key. The symbol represents an operation that is performed when the key is pressed. In the portable calculator environment, however, space is limited and a single symbol-to-key assignment is impractical. One solution is the use of a shift or modifier key. With multiple shift keys, each shift key is a different color and represents a set of symbols that are similarly colored, one symbol of each color adjacent each key. By pressing a blue shift key, for example, a user shifts a key's function to that of the adjacent blue symbol. A number of shift keys may be included in the keyboard and each key is thus associated with a number of functions. An example of a calculator employing shift keys is the Hewlett-Packard 15C.
Some portable calculators include keys labeled with alpha characters such as A, B, etc., for entering names, equations, and programs into the calculator. Methods for entering alpha characters by shifting to an "alpha mode" have been employed in prior calculators such as the Hewlett-Packard 41C. However, entering data with this technique has a number of drawbacks. For one, it requires frequent shifting between the alpha mode and other function modes because many of the functions which may also be entered share a key with an alpha character. For example, the letter A may share a key with other operations such as a cosine function or menu key assignment. Another drawback is finding the desired key on the keyboard. If more than a few symbols are associated with a key, one cannot discern with a glance which symbol is associated with each key. Both these drawbacks affect the speed and accuracy of entering data.
A variation on the shift technique is to assign several characters to a key, such as the letters A, B, and C. A character is then selected by shifting to this mode, pressing the key once, twice, or three times and pressing the enter key to confirm the entry.
One alternative is the provision of a separate alpha keyboard on a second face of a hinged calculator. Although adequate, such a calculator necessarily is larger than desirable for a hand-held calculator. Furthermore, the placement of the alpha keyboard on the second face remote from the display screen delays character entry. The user must glance first to the keyboard and then to the display screen in entering each character.
Another alternative is the "soft alpha" technique. In this technique, the alpha mode is entered by pressing a mode key to display groups of letters on the display screen above a set of unlabeled menu keys. The menu key corresponding to a group of letters that contains the desired letter is then pressed to associate one of each letters with a menu key. Pressing the menu key that corresponds to the desired letter then enters that letter. If the menu key for the group differs from the key for the single letter, the user must press two different keys to enter a letter. The primary drawback of "soft alpha" is the need to press different keys in sequence to enter a symbol such as an alpha character or a function. And while the "soft alpha" technique does not burden the nonmenu keys, it does require shifting between modes to access other menu key assignments.